Closing a reader attached to a grid

Starr Duskk
Starr Duskk used Ask the Experts™
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I have a grid which I populate by using a sqldatareader.

            grdSelector.DataSource = GetSource(blah)

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My GetSource consists of this, which returns a SqlDataReader

         Dim dr As SqlDataReader = Nothing
         Dim sql As String = GetQuery(Blah)
         Dim con As New SqlConnection(Name.GetConnectionString)
         Dim cmd As New SqlCommand(sql.ToString(), con)
         cmd.CommandType = CommandType.Text
         cmd.CommandTimeout = 600 
         con.Open()
         dr = cmd.ExecuteReader(CommandBehavior.CloseConnection) ' close the connection when the reader is closed
         Return dr

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Okay, so I set my reader to CloseConnection when the reader is closed. But when is the reader closed?

I am populating my grid with it using the grid.DataSource, but when is the reader closed? Is it automatically closed when the user leaves the page? Or do I need to specifically close that reader somewhere? If so, where and how?

thanks!
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Fernando SotoRetired
Distinguished Expert 2017
Commented:
Close it immediately after loading the grid.

Dim dr As SqlDataReader = GetSource(blah)
grdSelector.DataSource = dr
dr.Close()

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Most Valuable Expert 2012
Top Expert 2014

Commented:
I know this is unrelated to your question but would mention this in case you are not aware. Data reader is usually used when you want to either load a single record or loop through records to do some processing. For grids, using a table adapter to populate a datatable is usually a preferred method as it downloads all data simultaneously as opposed to data reader which only downloads one row at a time.
Starr DuskkASP.NET VB.NET Developer

Author

Commented:
Thank you CodeCruiser, I will change that. I assume that applies to populating comboboxes as well.
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Starr DuskkASP.NET VB.NET Developer

Author

Commented:
Also:

I don't define my datareader like this:
Dim dr As SqlDataReader = GetSource(blah)
grdSelector.DataSource = dr
dr.Close() 

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I call a method that returns a data reader like this:
 Dim daOrm As DataAccess.CustomDepartment = New DataAccess.CustomDepartment()
            grdSelector.DataSource = daOrm.GetDepartmentByClientIdSqlCommandReader(ClientId)

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Here is the gist of the method:
            Dim dr As SqlDataReader = Nothing
            Dim con As New SqlConnection(Name.GetConnectionString)
            Dim cmd As New SqlCommand(sql.ToString(), con)
            cmd.CommandType = CommandType.Text
            con.Open()
            dr = cmd.ExecuteReader(CommandBehavior.CloseConnection) ' close the connection when the reader is closed
            Return dr

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If I somehow use a using block around that, will it close the datareader or just the connection?

I believe I remember trying to put a using block around it before and when it loaded into my grid it had no values in it and was empty. I'd have to try again to see what happened, but pretty sure.

Any ideas for me rather than totally redoing all my grids? I guess I can, but would like to see if there's something I can do to salvage what I have. I already have to change to datatables.

thanks!
Most Valuable Expert 2012
Top Expert 2014

Commented:
Even dislike passing datareaders around even more as it creates risk of open connections and readers over time. If you do not have a lot of code at this stage, I would suggest change it.
Starr DuskkASP.NET VB.NET Developer

Author

Commented:
I saw this example which fills the DataTable and closes the connection. Is it necessary to close the datatable of the grid? or just the connection?

Public Function GetDataTable() As DataTable

            Dim query As String = "SELECT CustomerID, CompanyName, ContactName, ContactTitle, Address, PostalCode FROM Customers"

 

            Dim ConnString As [String] = ConfigurationManager.ConnectionStrings("NorthwindConnectionString").ConnectionString

            Dim conn As New SqlConnection(ConnString)

            Dim adapter As New SqlDataAdapter()

            adapter.SelectCommand = New SqlCommand(query, conn)

 

            Dim myDataTable As New DataTable()

 

            conn.Open()

            Try

                adapter.Fill(myDataTable)

            Finally

                conn.Close()

            End Try

 

            Return myDataTable

        End Function

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Starr DuskkASP.NET VB.NET Developer

Author

Commented:
Fernando SotoRetired
Distinguished Expert 2017

Commented:
Hi BobCSD;

To your question, "I saw this example which fills the DataTable and closes the connection. Is it necessary to close the datatable of the grid? or just the connection?", no you just close the reader, there is nothing to close on the DataGrid or DataTable.
Starr DuskkASP.NET VB.NET Developer

Author

Commented:
>>no you just close the reader

We are talking about my new scenario. I have been told not to use a reader and to use a DataTable instead. Plus, my scenario doesn't create the DataTable (or Reader) in the codebehind, it creates it in another library and passes it in. So I came up with a new change.

So looking at the suggested change from my last post, what do I need to make sure I do besides closing the connection? I do not close the DataTable anywhere. Nor do I close the Adapter.

ID: 39895363

thanks!
Fernando SotoRetired
Distinguished Expert 2017

Commented:
In connection to this post, "ID: 39895363", the way you are doing it there is correct.
Most Valuable Expert 2012
Top Expert 2014
Commented:
DataTable is disconnected so there is no need to "close" it.
Starr DuskkASP.NET VB.NET Developer

Author

Commented:
>>DataTable is disconnected so there is no need to "close" it.

Conversely, is a SQLDataReader not disconnected, so there is a need to close it?
Most Valuable Expert 2012
Top Expert 2014
Commented:
Yes SQLDataReader keeps the connection to database open and occupied until it is closed. It will become apparent if you try to execute another command using the same connection (you will get an error that an open reader is already attached to this connection).
Starr DuskkASP.NET VB.NET Developer

Author

Commented:
Thanks both of you! And thanks CC for the "not related to question" because evidentally it is, since a DataTable doesn't need closing and that's what I'm looking for. Something I don't have to close.

thanks!

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